Spain’s Rafael Nadal shakes the sweat off his head after winning his fourth round match of the French Open tennis tournament against Serbia’s Dusan Lajovic at the Roland Garros stadium, in Paris, France, Monday, June 2, 2014. Nadal won in three sets 6-1, 6-2, 6-1. (AP Photo/Michel Spingler)

Spain’s Rafael Nadal shakes the sweat off his head after winning his fourth round match of the French Open tennis tournament against Serbia’s Dusan Lajovic at the Roland Garros stadium, in Paris, France, Monday, June 2, 2014. Nadal won in three sets 6-1, 6-2, 6-1. (AP Photo/Michel Spingler)

Strapping tape is seen on Spain’s Rafael Nadal back during his fourth round match of the French Open tennis tournament against Serbia’s Dusan Lajovic at the Roland Garros stadium, in Paris, France, Monday, June 2, 2014. Nadal won in three sets 6-1, 6-2, 6-1. (AP Photo/Michel Spingler)

U.S pop singer Prince, top left and unidentified women, watch Spain’s Rafael Nadal playing Serbia’s Dusan Lajovic during their fourth round match of the French Open tennis tournament at the Roland Garros stadium, in Paris, France, Monday, June 2, 2014. (AP Photo/Darko Vojinovic)

Tennis fans, one draped in the Spanish flag, sit next to a sign reading “Paris is crazy about Rafa”, referring to Spain’s Rafael Nadal who played his fourth round match of the French Open tennis tournament against Serbia’s Dusan Lajovic at the Roland Garros stadium, in Paris, France, Monday, June 2, 2014. (AP Photo/Michel Spingler)

Spain’s David Ferrer reacts after defeating South Africa’s Kevin Anderson during their fourth round match of the French Open tennis tournament at the Roland Garros stadium, in Paris, France, Monday, June 2, 2014. Ferrer won 6-3, 6-3, 6-7, 6-1. (AP Photo/David Vincent)

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PARIS (AP) â€” Maybe, just maybe, Rafael Nadal was a tad vulnerable, the thinking went before this French Open.

He had lost three times on his beloved red clay already this year, more defeats than he ever had on the surface before heading to Roland Garros.

Then came an admission, after the Grand Slam tournament’s third round, that his back was bothering him and slowing his serves.

Well, leave it to the eight-time French Open champion’s upcoming quarterfinal opponent â€” 2013 runner-up David Ferrer, one of the men who beat Nadal on clay this spring â€” to set the record straight.

“Rafael,” Ferrer said, “is always the favorite.”

Nadal certainly looked the part in the fourth round Monday, when he won 18 points in a row during one stretch en route to beating 83rd-ranked Dusan Lajovic of Serbia 6-1, 6-2, 6-1 for a record 32nd consecutive victory at the French Open. That broke Nadal’s own mark of 31 and moved him a step closer to a fifth straight title in Paris.

The No. 1-ranked Nadal, now 63-1 for his career at the tournament, has won all 12 sets he’s played in Paris in 2014, dropping a total of 23 games. He was asked whether he would have preferred a more taxing encounter by now.

And his back? The one that flummoxed him during a loss in the Australian Open final in January, and then acted up Saturday, leading to an average first serve of 102 mph (165 kph) and top speed of 114 mph (184 kph)? It didn’t appear to be as much of an issue against Lajovic: Nadal averaged 107 mph (173 kph), with a high of 119 mph (192 kph).

“My back can be pretty unpredictable,” said Nadal, who wore thick vertical strips of athletic tape under his shirt. “I’m not lying. It’s totally unpredictable. I don’t want to speak too much about it.”

Last year’s French Open final is one of 21 losses for Ferrer in 27 matches against fellow Spaniard Nadal. But Ferrer won their most recent meeting in straight sets, on April 18 at the Monte Carlo Masters.

As Ferrer himself noted, though, that was a best-of-three-set match. They’ll be playing best-of-five on Wednesday.

“Tactically, I will have to be perfect,” Ferrer said. “I hope that I will instill some doubts in Rafa’s mind, but if we play at our best level, both of us, he will be a better player.”

The other quarterfinal on the top half of the draw will be Wimbledon champion Andy Murray against 23rd-seeded Gael Monfils of France.

No. 7 Murray beat No. 24 Fernando Verdasco of Spain 6-4, 7-5, 7-6 (3) in a match marked by a wild third set. Verdasco held to get within 4-3 with an apparent service winner, but chair umpire Pascal Maria said that point should be replayed because a line judge called the ball out. That prompted Verdasco to begin berating Maria, shouting “Are you kidding me?” and saying he wanted a tournament supervisor to intervene â€” until Murray conceded the point.

Later, Verdasco said he’s had several bad experiences with Maria.

“He’s not the kind of umpire I get along with, I can tell you that,” Verdasco said.

Monfils advanced with a much more staid 6-0, 6-2, 7-5 win against 41st-ranked Guillermo Garcia-Lopez of Spain.

“I played aggressive,” Halep said after defeating the last American singles player left in the tournament, No. 15 Sloane Stephens, 6-4, 6-3. “I dominated the match, I think.”

Petkovic’s 1-6, 6-2, 7-5 victory over 148th-ranked Kiki Bertens of the Nertherlands was the only three-setter for women on Monday, a two-hour struggle filled with 77 unforced errors and 14 service breaks.